Floating roof having uniformly distributed buoyancy means

ABSTRACT

A Floating roof for covering liquid products stored in storage tanks or the like wherein the roof has an upper surface and a lower surface, with the lower surface in substantially continuous contact with the stored product. Buoyancy means are connected to the floating roof and are substantially uniformly distributed with respect thereto to float the roof on the stored product in the event the stored product leaks onto the surface of the floating roof, and to prevent sinking thereof beyond a predetermined amount and to minimize uneven settling of the roof in the stored product.

United States Patent 1191 Edwards et a1.

[54] FLOATING ROOF HAVING [451 Apr. 3, 1973 1,698,158 1/1929 1,819,4018/1931 2,297,985 10/1942 3,313,443 4/1967 Dial et al. ..220/26 R FOREIGNPATENTS OR APPLICATIONS 1,495,530 10/1967 France ..220/26 R 789,3667/1968 Canada..... ...........220/26 R 1,230,046 9/ 1960 France ..220/26R 895,820 5/1962 Great Britain ..220/26 R 1,060,941 3/1967 Great Britain..220/26 R Primary Examiner-Lloyd L. King Attorney-Shoemaker and Mattare[57] ABSTRACT with respect thereto to float the roof on the storedproduct in the event the stored product leaks onto the surface of thefloating roof, and to prevent sinking thereof beyond a predeterminedamount and to minimize uneven settling of the roof in the storedproduct.

25 Claims, 8 Drawing Figures UNIFORMLY DISTRIBUTED BUOYANCY MEANS [75]Inventors: Norman W. Edwards, Sewickley; Vincent H. Derr, Coraopolis;Richard A. Mattson, Sewickley, all of Pa.

[73] Assignee: Pittsburgh-Des Moines Steel Company, Pittsburgh, Pa.

[22] Filed: Apr. 13, 1971 [21] Appl. No.: 133,557

[521 US. Cl. ..220/26 R [51] Int. Cl. ..B65d 87/18 [58] Field of Search..220/26 R, 26 S; 9/11 R, 12; 114/123 [56] References Cited UNITEDSTATES PATENTS 1,574,011 2/1926 Wiggins ..220/26 s 135,784 2/1873 Davies..9/l1 R 3,237,414 3/1966 Straub et al ..9/11 R 2,660,194 11/1953Hoffman ..220/26 R 3,424,335 1/1969 Wiltshire ..220/26R 3,288,32211/1966 Marshall et a1. ..220/26R 3,338,454 8/1967' Nelson ..220/26 SPATENIEDAPR 3 1975 SHEET 1 0F 2 FIG. 3.

INVENTORS- NORMAN W. EDWARDS VINCENT H. DERR 8a 7 RICHARD A. MATTSON ifg M1 )H m ATTORNEYS FLOATING ROOF-HAVING UNIFORMLY DISTRIBUTED BUOYANCYMEANS BACKGROUND OF THE INVENTION and the like stored in large storagetanks or the like.

The floatingiroof has an upper surface and a lower surface, and thelower surface is in substantially continuous contact with the storedproduct so as to prevent contamination of the stored product, oraccumulation of vapors, for example, which would create a hazardoussituation if a volatile product is stored and the vapors are allowed toaccumulate. Buoyancy means are connected to the roof and aresubstantially uniformly distributed with respect thereto to provide asubstantially uniformly distributed buoyant force to float the roof onthe stored product in the event stored product leaks onto the surfacethereof.

With the present invention, the buoyancy means does not provide anybuoyant force so long as the roof or cover means is leak tight, and theroof floats as a pan roof or as a shallow dish floating on the storedproduct, with the roof simply displacing sufficient stored product untilthe buoyant force equals its weight. When a rupture occurs in the roof,the stored product leaks onto the surface thereof and the whole roofsettles in the stored product. The mode of floatation of the roof thenchanges and the buoyancy means provide substantially uniform support ofthe roof, with the displaced volume then equaling the volume occupied bythe buoyancy means and the additional volume occupied by the pontoon.This prevents sinking of the roof beyond a predetermined amount,minimizes uneven settling of the roof in the stored produce, and insurescontinuous contact between the roof and stored product.

Conventional floating roof structures comprise a relatively thin coveror deck made of a plurality of secured together plates with a largepontoon or buoyancy means secured thereto around the outer peripherythereof. During normal operation, the cover as well as the pontoon floaton the stored product. In the event of a rupture occurring in the coverand leakage of stored product'onto the surface thereof, the pontoonprovides support for the cover to prevent it from sinking in the storedproduct. The pontoon must have sufficient buoyancy to float itself andthe deck or cover. Further, thepontoon must have sufficient structuralrigidity and strength to resist theloads applied thereto from the weightof the cover, which would include both horizontal and vertical forcecomponents acting on the pontoon. The horizontal or radial componentsproduce compressive stresses in the pontoon and the pontoon musttherefore be designed as a ring subjected to an axisymmetric radialload. The magnitude of the radial load increases with the diameter ofthe roof and such roofs have diameters up to 300 feet or more. Since thepontoon is usually fabricated of relatively thin material, as forexample, materials having a thickness in the range of three-sixteenthsof an inch to five-sixteenths of an inch, and since the stress is com-.

pressive, not all of the pontoon cross-section is effective. inresisting the applied loads for the size of the roof for which thepontoon would be used.

As the pontoon width is increased in order to provide more buoyancy tofloat the cover, the cross-sectional area of the pontoon effective toresist the compressive stresses and the effective moment of ineria ofthe pontoon remains essentially unchanged. For the larger tanks, say forexample, those having a diameter of 300 feet, the effectivecross-sectional area of the pontoon is not sufficient to satisfy thestructural requirements. Accordingly, additional stiffening means isadded to the pontoon in conventional structures. This is satisfactoryfor tanks whose diameters are greater than about 200 feet, but is anexpensive solution and also may not be practical for tanks having adiameter in excess of 300 feet.

With conventional cover or floating roof structures, the roof sags inthe center thereof when product spills onto the top thereof as when arupture occurs in the roof, the roof being supported about its peripheryby the pontoon. The amount of sag or deflection of the roof for largertanks often exceeds 40 inches. As a result, the cover of a conventionalfloating roof is often permanently distorted when a rupture occurs andthe stored product leaks onto the surface thereof causing deflection ofthe cover.

The present invention provides a floating roof having substantiallyuniformly distributed buoyancy means connected thereto to providesubstantially uniform floating support of the roof in the event of arupture in the roof and leakage of stored product onto the surfacethereof. Accordingly, since the weight to be supported is substantiallyuniformly distributed, uniform distribution of the buoyancy means forsupporting the roof in the event of leakage of stored product onto thesurface thereof results in even distribution of stresses throughout theroof structure and eliminates the need for a large buoyancy ring orpontoon around the periphery of the roof.

The required buoyancy is provided by leaktight buoys or buoy unitsarranged on top of the, roof and evenly spaced on a repeating regulararrangement. The ring around the periphery of the roof serves primarilyas a small structural member to keep the roof round and to provide meansfor attachment of the roof seal. The ring does'i'mpart some buoyancy tothe roof, however, but the roof is not supported entirely by the annularbuoyancy ring or pontoon when product leak's onto the surface thereof asin the conventional constructions. Accordingly, when a leak occurs withafloating roof according to the present invention, and the stored productleaks onto the surface thereof, the roof will settle uniformly in theproduct to a predetermined depth depending on the buoyancy imparted tothe cover by the buoyancy means distributed thereover. When the leak orrupture in the cover is repaired, the floating roof will look andfunction the same as when it was'new and there will be no distortion ofthe roof as in the conventional constructions. A floating roof structurein accordance with the invention is thus exceptionally reliable and issimple and economical in construction.

Specifically, the buoyancy means for supporting the floating roofaccording to the present invention comprise a plurality of separate andindependent buoyant modules or units attached to the top surface of thefloating roof and evenly spaced on the roof in a regular arrangement -ina manner such that each buoy unit floats or supports a predeterminedportion of the floating roof, with adjacent buoys supporting adjacentareas of the roof and all of the buoys together providing sufficientbuoyancy to float the entire roof. The buoys may be made of any suitablemetallic or non-metallic, organic or non-organic material having anysuitable shape. For example, the buoys can be made as hollow vessels ofaluminum, steel or fiberglass or the like, or they may comprise blocksof foam or like buoyant material. It is only necessary that the buoysand the roof be chemically compatable with the stored product.Preferably, the buoys are attached to the top side of the roof, but theymay extend through the roof and down into the stored product a slightamount, if desired, so long as the roof remains in continuous contactwith the stored product.

The roof itself may be made of steel or aluminum or any other materialsuch as fiberglass or the like so long as it is compatable with thestored product and has sufficient strength to be suspended betweenadjacent buoys in the event of a leak occurring in the roof.

OBJECTS OF THE INVENTION It is an object of this invention to provide afloating roof structure for covering products stored in large storagetanks or the like wherein the roof is in substantially continuouscontact with the stored product.

Another object of this invention is to provide a floating roof structurewherein buoyancy means are substantially uniformly distributed and fixedto the floating roof for floating the roof on the stored product in theevent of stored product leaking onto the surface of the floating roof.

An even further object of this invention is to provide a floating roofhaving buoyancy means for floating the roof on stored product when thestored product leaks onto the surface thereof wherein the buoyancy meansis attached to the top side of the floating roof.

A more specific object is to provide a floating roof structure whereinbuoyancy means are provided for floating the roof on stored product inthe event that stored product leaks onto the surface thereof, saidbuoyancy means being evenly spaced and distributed over the roofstructure and attached to the top side thereof, said buoyancy meanscomprising a plurality of independent buoys each of which floats orsupports a predetermined portion of said cover structure when productleaks onto the surface thereof and said roof settles in the storedproduct, with the buoyancy means distributed in a repeating regulararrangement.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a top schematic perspectiveview of a roof in accordance with the present invention showing thearrangement of buoys thereon.

FIG. 2 is a sectional view taken along line 2-2 in FIG. 1.

FIG. 3 is a top plan view of one form of buoy means.

FIG. 4 is a view in section of a modified buoy means.

FIG. 5 is a sectional view of another modified form of buoy means,wherein the buoy means extends through the roof.

FIG. 6 is a sectional view similar to FIG. 2 showing a modified form ofannular ring or pontoon and seal means around the periphery of the roof.

FIG. 7 is an enlarged sectional view similar to FIG. 6 showing a furtherform of annular ring and seal means.

FIG. 8 is a top perspective view of a third form of buoy means.

DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings,wherein like reference numerals indicate like parts throughout theseveral views, a floating roof structure in accordance with theinvention is indicated generally at 1 in FIG. 1. The floating roofcomprises a cover 2 made up of a plurality of individual rectangularplates 3 welded or otherwise suitably secured together along adjacentedges. An annular tubular ring or pontoon 4 is secured about the outerperiphery of the cover 2. As seen in FIG. 1, the plates 3 are staggeredor offset longitudinally relative to one another so that the jointsbetween adjacent plates are not in alignment with one another. Theannular ring 4 imparts a certain amount of buoyancy to the cover andprovides support for the peripheral portion thereof, and in addition itmaintains the cover in a round shape and provides a means for attachmentof a seal means.

A plurality of individual buoyancy means or buoys 5 are attached to thetop surface of the cover 2. The buoys 5 are arranged near opposite endsof each of the plates 3 in alternate rows 6 of plates in the cover, withthe intermediate rows 7 of plates 3 not having any buoys attachedthereto. Each buoy 5 has sufficient size and buoyancy to float itselfand a predetermined portion of the cover 2, as indicated in phantomlines at 8, and with the buoys evenly spaced over the cover in arectangular grid arrangement so that buoyancy is imparted uniformly tothe entire cover sufficient to float the cover on a stored product P inthe event a leak occurs in the cover and the stored product leaks ontothe surface thereof. As shown in FIG. 2, the buoyancy means impartsufficient buoyancy to the roof to prevent it from sinking-beyond thelevel indicated in phantom line at L in the event a rupture occurs inthe roof and stored product leaks onto the surface thereof.

As best seen in FIG. 2, each buoy 5 comprises a relatively shortcylinder 9 welded at one end 10 to the top of the plates 3 comprisingthe cover 2, and a flat plate or cover 11 welded to the other or top end12 of cylinder 9 to define a closed volume 13 filled with a buoyantmaterial such as air or foam or the like. The opposite edges of each ofthe plates 3 are overlapped a predetermined amount d, such as forexample 1 inch, and are suitably secured together such as by welding wor the like. The annular ring 4 is suitably secured such as by weldingor the like about the periphery of the cover 2 with the cover secured tothe annular ring 4 at its mid portion by means of a short, radiallyextending flange l4 welded between the ring 4 and plates 3. A suitableseal means indicated generally at 15 is secured about the outerperiphery of the floating roof for sealing engagement with the side wallof a tank T or the like in which the floating roof is disposed. The sealmeans 15 includes a relatively narrow or short annular connecting memberor web 16 secured as by welding or the like to the mid-portion of tube 4and extending radially outwardly therefrom. A vertically disposed,annular, cylindrical support wall 17 is secured intermediate its upperand lower edges to the web 16 and has a vertical dimension approximatelyequal to the diameter of ring '4. A scuff band is, formed of-a suitableflexible and The cover 11 of buoy 5 is shown ashaving an oc-' tago nalshape in FIG. 3 and projects a-slight amount beyond the outer peripheryof the cylinder 9. The cover 11 and buoy side wall 9 could have anyshape other than that shown, as desired, or the buoy could comprise ablock of foam material or the like as at 20 in FIG. 4, suitably attachedto the top side of the cover 2.

Referring now to FIG. 5, a slightly modified buoy means 5' isillustrated and comprises atubular side wall 9' with a top cover 11 anda bottom cover 21 welded to opposite ends thereof. The buoy 5 is filledwith a suitable buoyant material 22 such as foam or the like and extendsthrough an opening 23 in the plate 3 and projects below the plate 3 adistance D. The distance D may be varied, so long as the buoy 5' doesnot extend below the plate 3 an amount sufficient to float the plate 3above the surface of the product stored therebeneath; and for a typicaltank, the distance D would be approximately 2 or 3 inches.

A modified annular buoyancy ring or pontoon 24 is shown in FIG. 6, andhas a generally trapezoidal crosssectional shape and comprises an inner,annular cylindrical wall 25 welded or otherwise suitably securedintermediate its upper and lower edges to a short, radially extendingflange 14, which is secured to the periphery of cover 2, and a radiallyoutwardly spaced annular cylindrical wall 26 of greater verticaldimension than wall 25 and having a radially inwardly offset portion 27at the lower marginal edge thereof defining a clearance recess or notch28. An upper, slightly inclined annular wall or plate 29 is welded orotherwise suitably secured to the top marginal edges of walls 25 and 26and extends slightly beyond the plates of walls 25 and 26 at its innerand outer peripheral edges 30 and 31, respectively. A similar slightlyinclined annular wall or plate 32 is welded or otherwise suitablysecured to the bottom marginal edges of the radially offset wall 27 andwall 25 and extends slightly beyond the planes of walls 27 and 25 at itsinner and outer peripheral edges 33 and 34, respectively. A relativelynarrow, radially extending wall 35 joins the upper marginal edge of wall27 and wall 26 spaced upwardly from the bottom marginal edge thereof todefine a downwardly extending, annular bolting flange 36. A scuff band37 of a suitable flexible and wear resistant material is connected as bybolts or the like (not shown) at its upper marginal edge to the outerperipheral edge 31 of plate 29 and is connected at its bottom marginaledge to bolting flange 36 as by bolts or the like (not shown). Asuitable, annular, tubular, expandable seal ring 38 is enclosed withinand supported by the scuff band 37 for effecting a sliding seal betweenthe floating roof and the side wall of tank T. The construction shown inFIG. 6 could be used, for

example, on tanks having a diameter of up to about 300 shown and issubstantially identical with the pontoon shown in FIG. 6 except thatannular, circumferentially extending stiffening angles 39 and 40 arewelded or otherwise suitably secured approximately medially of the topand bottom annular plates 29 and 32 to impart additional stiffeningthereto. This embodiment of pontoon could be used for example on tankshaving a diameter of about 300 feet or less.

In FIG. 8, a further form of buoy 5' is shown and rather than beingcircular with an octagonal cover 11 thereon as shown in FIG. 3, the buoy5' is rectangular in cross-section with substantially flat, rectangularside walls 9 and with a square or rectangular cover 11' welded orotherwise suitably secured over the top thereof. The buoy 5 is attachedto the top surface of plate 3 as in the FIGS. 2 and 3 embodiment, butcould extend through the plate as in the FIG. 5 embodiment, if desired.

In a typical tank constructed in accordance with the present invention,the plates 3 would be approximately 30 feet long, 7 a feet wide and 3/16to 5/16 of an inch thick. Adjacent plates would be welded together withtheir adjacent edges overlapped approximately 1 inch, and on a tankhaving a diameter of about 280 feet, approximately 241 buoys would beused, with the buoys attached to the top surface of the plates 3 andequally spaced approximately 15 feet apart in a rectangular gridarrangement. The annular buoyancy ring or pontoon would be approximately3 feet wide and each buoy would be approximately 3 feet high and 5 feetwide. For a tank having a diameter of about 340 feet, approximately 365buoys wouldbe used in the cover.

Obviously, either the pontoon as shown in FIG. 2 or as shown in FIGS. 6and 7 could be used on the floating roof or any other suitable pontooncould be used Further, the buoys could have any suitable shape and sizeand any suitable material could be used, and the buoys'could be'arrangedin any-regular manner relative to the roof so long as the buoyancy meansfor floating the roof is evenly distributed with respect thereto andprovide uniform support of the roof in the event the roof ruptures andstored product leaks onto the surface thereof. For example, buoys ofdiflerent sizes may be placed in lines extending radially from thecenter of the roof. The individual buoys are fabricated, welded orotherwise suitably secured to the plates 3, and leak tested in the shopprior to shipment to the field, thus minimizing the amount of field workand substantially reducing the cost of the floating roof.

As this invention may be embodied in several forms without departingfrom the spirit or essential characteristics thereof, the presentembodiment is therefore illustrative and not restrictive, since thescope of the invention is defined by the appended claims rather than bythe description preceding them, all changes that fall within the metesand bounds of the claims or that form their functional, as well asconjointly cooperative equivalents, are therefore intended to beembraced by those claims.

We claim:

l. A floating roof for covering liquid stored in storage tanks or thelike wherein the roof floats on the stored liquid, said roof having anupper surface and a lower surface, said lower surface in continuouscontact with the stored liquid to prevent the formation and ac buoyancymeans connected to the floating roof only on the upper surface thereofuniformly distributed with respect thereto to provide uniform floatingsupport of the floating roof and to prevent sinking of the roof beyond apredetermined amount and to minimize uneven settling of the roof in thestored liquid in the event of a rupture in the roof and leakage of thestored liquid onto the surface thereof.

2. A floating roof as in claim 1, wherein said buoyancy means comprisesa plurality of individual and separate buoys attached to said roof in aregular arrangement, each of said buoys having a size and buoyancy suchas to float a predetermined portion of said roof and all of said buoystogether providing sufficient buoyancy to uniformly float the entireroof.

3. A floating roof as in claim 2, wherein the lower surface of saidfloating roof is-substantially flat and planar.

4. A floating roof as in claim 3, wherein said buoys are tubular, oneend of each of said tubular buoys attached to the upper surface of saidroof and a substantially flat planar top closing the other end of saidbuoys to define an enclosed buoyant volume within each of said buoys.

5. A floating roof as in claim 4, wherein each of said buoys is filledwith a foam material.

6. A floating roof as in claim 2, wherein said buoys comprise blocks offoam material.

7. A floating roof as inclaim 25, wherein said buoys extend throughopenings in said floating roof and project a slight amount below theroof.

8. A floating roof as in claim 7, wherein said buoys are tubular, withthe opposite ends thereof closed by substantially flat plates or coversto define a closed buoyant volume.

9. A floating roof as in claim 8, wherein said buoys are filled with afoam material.

10. A floating roof as in claim 3, wherein said buoys are cylindrical.

11. A floating roof as in claim 11, wherein one end of each of saidbuoys is attached to said roof and a substantially flat cover closes theother end of said buoys, said cover having a polygonal shape.

12. A floating roof as in claim 3, wherein said buoys are rectangular incross-section.

13. A floating roof as in claim 2, wherein an annular pontoon isconnected to said floating roof around the periphery thereof.

14. A floating roof as in claim 13, wherein said pontoon is circular incross-section.

15. A floating roof as in claim 13, wherein said pontoon has asubstantially trapazodial cross-section.

16. A floating roof as in claim 15, wherein said pontoon comprises asubstantially vertically disposed cylindrical inner wall and a radiallyoutwardly spaced substantially vertically disposed cylindrical wall,said outer wall having a greater vertical dimension than said innerwall, and slightly inclined annular top and bottom walls attached to thetop and bottom edges of said inner and outer walls, respectively, saidinner wall being secured intermediate its top and bottom edges to theperiphery of said roof.

17. A floating roof as in claim 16, wherein circumferentially extendingstiffeners are secured to each of said top and bottom annular walls forstiffening and reinforcirtrg the pontoon. l

18. A oating roof as 111 claim 2, wherein said roof comprises aplurality of substantially rectangular plates welded or otherwisesuitably secured together along adjacent edges thereof.

19. A floating roof as in claim 18, wherein said plates are overlappedat adjacent edges.

20. A floating roof as in claim 19, wherein said plates arelongitudinally offset relative to one another so that joints betweenadjacent plates are not aligned.

21. A floating roof as in claim 13, wherein seal means is connected tosaid floating roof about the periphery thereof.

22. A floating roof as in claim 21, wherein said seal means comprises ascuff band connected to the top and bottom edges respectively of asupport means on said .pontoon, and an annular flexible tube seal issupported in said scuff band for effecting a sliding seal between thewall of said tank and said floating roof.

23. A floating roof as in claim 20, wherein said plates are arranged inrows, and said buoys are attached to alternate rows of plates.

24. A floating roof as in claim 23, wherein said buoys are attached tosaid plates in said alternate rows in evenly spaced relationship to oneanother, with two buoys attached to each plate in said alternate rows.

25. A floating roof for covering liquid stored in storage tanks or thelike wherein the roof floats on the stored liquid, said roof having anupper surface and a lower surface, said lower surface in substantiallycontinuous contact with the stored liquid, a plurality of buoyancy meansconnected to the floating roof with at least a major portion of eachbuoyancy means positioned above the lower surface of the roof, saidbuoyancy means substantially uniformly distributed with respect to thefloating roof to provide uniform floating support of the floating roofand to prevent sinking of the roof beyond a predetermined amount and tominimize uneven settling of the roof in the stored liquid in the eventof a rupture in the roof and leakage of the stored liquid onto thesurface thereof.

# l i i t

1. A floating roof for covering liquid stored in storage tanks or thelike wherein the roof floats on the stored liquid, said roof having anupper surface and a lower surface, said lower surface in continuouscontact with the stored liquid to prevent the formation and accumulationof vapor therebeneath and/or to prevent contamination of the storedliquid, a plurality of buoyancy means connected to the floating roofonly on the upper surface thereof uniformly distributed with respectthereto to provide uniform floating support of the floating roof and toprevent sinking of the roof beyond a predetermined amount and tominimize uneven settling of the roof in the stored liquid in the eventof a rupture in the roof and leakage of the stored liquid onto thesurface thereof.
 2. A floating roof as in claim 1, wherein said buoyancymeans comprises a plurality of individual and separate buoys attached tosaid roof in a regular arrangement, each of said buoys having a size andbuoyancy such as to float a predetermined portion of said roof and allof said buoys together providing sufficient buoyancy to uniformly floatthe entire roof.
 3. A floating roof as in claim 2, wherein the lowersurface of said floating roof is substantially flat and planar.
 4. Afloating roof as in claim 3, wherein said buoys are tubular, one end ofeach of said tubular buoys attached to the upper surface of said roofand a substantially flat planar top closing the other end of said buoysto define an enclosed buoyant volume within each of said buoys.
 5. Afloating roof as in claim 4, wherein each of said buoys is filled with afoam material.
 6. A floating roof as in claim 2, wherein said buoyscomprise blocks of foam material.
 7. A floating roof as in claim 25,wherein said buoys extend through openings in said floating roof andproject a slight amount below the roof.
 8. A floating roof as in claim7, wherein said buoys are tubular, with the opposite ends thereof closedby substantially flat plates or covers to define a closed buoyantvolume.
 9. A floating roof as in claim 8, wherein said buoys are filledwith a foam material.
 10. A floating roof as in claim 3, wherein saidbuoys are cylindrical.
 11. A floating roof as in claim 11, wherein oneend of each of said buoys is attached to said roof and a substantiallyflat cover closes the other end of said buoys, said cover having apolygonal shape.
 12. A floating roof as in claim 3, wherein said buoysare rectangular in cross-section.
 13. A floating roof as in claim 2,wherein an annular pontoon is connected to said floating roof around theperiphery thereof.
 14. A floating roof as in claim 13, wherein saidpontoon is circular in cross-section.
 15. A floating roof as in claim13, wherein said pontoon has a substantially trapazodial cross-section.16. A floating roof as in claim 15, wherein said pontoon comprises asubstantially vertically disposed cylindrical inner wall and a radiallyoutwardly spaced substantially vertically disposed cylindrical wall,said outer wall having a greater vertical dimension than said innerwall, and slightly inclined annular top and bottom walls attached to thetop and bottom edges of said inner and outer walls, respectively, saidinner wall being secured intermediate its top and bottom edges to theperiphery of said roof.
 17. A floating roof as in claim 16, whereincircumferentially extending stiffeners are secured to each of said topand bottom annular walls for stiffening and reinforcing the pontoon. 18.A floating roof as in claim 2, wherein said roof comprises a pluralityof substantially rectangular plates welded or otherwise suitably securedtogether along adjacent edges thereof.
 19. A floating roof as in claim18, wherein said plates are overlapped at adjacent edges.
 20. A floatingroof as in claim 19, wherein said plates are longitudinally offsetrelative to one another so that joints between adjacent plates are notaligned.
 21. A floating roof as in claim 13, wherein seal means isconnected to said floating roof about the periphery thereof.
 22. Afloating roof as in claim 21, wherein said seal means comprises a scuffband connected to the top and bottom edges respectively of a supportmeans on said pontoon, and an annular flexible tube seal is supported insaid scuff band for effecting a sliding seal between the wall of saidtank and said floating roof.
 23. A floating roof as in claim 20, whereinsaid plates are arranged in rows, and said buoys are attached toalternate rows of plates.
 24. A floating roof as in claim 23, whereinsaid buoys are attached to said plates in said alternate rows in evenlyspaced relationship to one another, with two buoys attached to eachplate in said alternate rows.
 25. A floating roof for covering liquidstored in storage tanks or the like wherein the roof floats on thestored liquid, said roof having an upper surface and a lower surface,said lower surface in substantially continuous contact with the storedliquid, a plurality of buoyancy means connected to the floating roofwith at least a major portion of each buoyancy means positioned abovethe lower surface of the roof, said buoyancy means substantiallyuniformly distributed with respect to the floating roof to provideuniform floating support of the floating roof and to prevent sinking ofthe roof beyond a predetermined amount and to minimize uneven settlingof the roof in the stored liquid in the event of a rupture in the roofand leakage of the stored liquid onto the surface thereof.